Heretofore, a measurement device that measures an AC voltage applied to a conductor in an electric wire coated with an insulator has been proposed. This measurement device has been disclosed in, for example, Patent Document 1. The technology relating to the measurement device disclosed in Patent Document 1 is outlined below. Note that the reference numerals used in recitations relating to Patent Document 1 are the reference numerals recited in the embodiments of Patent Document 1 and are different from reference numerals used hereafter in the embodiments of the present application.
At least two capacitors 13 and 14 with different capacitance values are provided. The at least two capacitors 13 and 14 with different capacitance values are selectively connected between a detector probe and a common potential point. A coupling capacitance 12 is formed between the detector probe and a conductor to which a voltage to be measured is being applied. The voltage to be measured is voltage-divided by a voltage division circuit that is structured by the selectively connected capacitor 13 or 14 and the coupling capacitance 12. The connection is switched between the selectively connected capacitors 13 and 14, the coupling capacitance 12 is computed from values of the divided voltages when the two different capacitors are connected and the capacitance values of the two capacitors, and the voltage to be measured is found from the computed coupling capacitance 12.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2003-028900